1. Field of the Invention
This invention relates to a laboratory material and, more particularly, to a stable enzyme reference composition.
2. Description of the Prior Art
Various compositions capable of being employed in conjunction with the analysis of enzymes, to either calibrate a instrument or to periodically verify that the instrument is still operating within the tolerances desired, are known to those skilled in the art.
For example, U.S. Pat. No. 3,466,249 (hereinafter referred to as Anderson) discloses a blood serum reference standard comprising a first container of freeze-dried blood serum and a second container of aqueous ammonium bicarbonate. The final pH of Anderson's reconstituted serum is 7.5.+-.0.5. This pH range is felt by Anderson to be within an acceptable range for test systems as well as for stability of the reconstituted serum's components, particularly the enzymes.
U.S. Pat. No. 3,629,142 (hereinafter referred to as Marbach) discloses a freeze-dried serum reference standard comprising blood serum and a carbonate or bicarbonate of tris(hydroxymethyl)aminomethane which is reconstituted by the addition of distilled water. The tris carbonate imparts a normal pH to the serum so as to provide for the stability of its constituents, and particularly the enzymes. (For normal serum and plasma that are collected under routine conditions, the normal pH range is generally considered to be about 7.3 to about 7.45. See Tietz, Fundamental of Clinical Chemistry, W. B. Saunders Co., Philadelphia, Pa. (1970), pg. 634; and Henry et al., Clinical Chemistry, Principles and Technics, 2nd Edition, Harper & Row, New York, N.Y. (1974), pgs. 774-778.)
U.S. Pat. No. 3,876,375 and 4,121,905 (hereinafter referred to Maurukas I and Maurukas II) disclose a biological reference control composition comprising in its non-biological compound from about 60 to about 80 weight percent water and from about 20 to about 40 weight percent of at least one alkylene polyol having from 2 to 5 carbon atoms, the remainder being chiefly at least one natural biological material selected from the group consisting of blood serum, enzyme, metabolites, electrolytes, and hormones. Although the pH of this composition is not disclosed in either Maurukas I or Maurukas II, experiments have shown the pH to be from about 8.3 to about 8.5.
One short coming of the above prior art composition is that their enzyme constituents are highly unstable. For example, the manufacturer of a commercial composition believed to be within the scope of Marbach, supra, recommends that determinations of enzyme constituents of its distilled or deionized water reconstituted serum be made only on the day that the serum is reconstituted.
Similarly, the manufacturer of a commercial composition within the scope of Anderson also recommends that the determinations of its reconstituted composition be made only on the day that the serum is reconstituted.
Both of the above reconstituted compositions are recommended by their manufacturer to be stored between 2.degree. and 8.degree. C.